The reaction CH2CH2 + H2 → CH3CH3 is an example of

The choices can be found elsewhere and as follows:

(1) substitution

(2) esterification

(3) addition

(4) fermentation

I believe the correct answer is option 3. The reaction CH2CH2 + H2 → CH3CH3 is an example of an addition reaction. It is a reaction where two or more molecules combine to form a larger one. Hope this answers the question.